This is about the noise fans make when they are displeased. This is about the nightly referendum at professional sports contests.

Whom do you cheer? Whom do you boo? And why?

This week, Jonathan Papelbon became the latest former Boston sports star to feel the wrath of fans who once worshipped at his size-13 feet. Pap returned to Fenway with the Philadelphia Phillies and was roughed up by Hub fans when he came out of the bullpen to face the Red Sox in the ninth.

Emotionally, this makes sense. I guess.

Being a fan is an emotional experience. It does not require reason or common sense. Cheering and jeering is all about laundry, right? Booing is on the fans’ Bill of Rights.

Still, booing Papelbon seems too dumb for words. It’s sort of like booing Johnny Damon when he came to town with the Yankees or booing Adam Vinatieri when he lines up for a field goal while wearing a Colts uniform.

Looking for answers, I went to Kevin Youkilis before Friday night’s game at Yankee Stadium, a 4-1 New York victory. Youk knows all about cheers and boos. He was a member of the Red Sox from 2004 until the middle of 2012.

He was standing in the infield when Damon came back with the Yankees and got crushed by Sox fans in 2006. He was on the other side last summer when he came back with the White Sox.

And let’s not forget that Youk is a lifelong Cincinnati Bengals fan who is married to Tom Brady’s sister. Youk knows football. He knows Bengals fans always hated James Harrison. Until now.

And he knows Boston fans.

“Nothing surprises me,’’ Youk said when I told him about Papelbon. “Ted Williams got booed in Boston. It doesn’t matter who you are.’’

What did he think of the treatment Damon got when he returned to Fenway with the Yankees?

“Guys have feelings,’’ said Youkilis, who had been on the shelf since April 27 with a lower back strain. “You’re not just this robot that goes out there.

“I think Johnny really loved Boston and he wanted to come back. But it’s a business, and there’s two sides to every story. Johnny said that he had an offer and they didn’t bite on it and they played hardball and they lost.

“It’s half and half. Johnny got some cheers when he came back. You can’t worry about the negative. You’ve got to worry about the people that love you.

“The people that hate you? You can’t change their minds. I would say there’s 20 percent that can make it sound like the other 80 percent are booing.’’

Booing some players makes perfect sense. On Wednesday at the Garden, the Bruins will play Game 3 against the Pittsburgh Penguins in their conference final series. Pittsburgh’s Jarome Iginla and Matt Cooke will be roasted every time they touch the puck. This makes sense. Iginla chose the Penguins over the Bruins when he had a chance to come to Boston. He said the Penguins had a better chance to win a Stanley Cup. He dissed the B’s and the Hub.

Cooke is even worse. He ended Marc Savard’s career with a nasty blow to the head. He is a dirty player, still employed by the team he was with when he committed the act. Booing Cooke makes sense.

On some level, I suppose booing Ray Allen also makes sense, thought it strikes me as wildly immature. Allen chose the Miami Heat over the Celtics. He took less money. But it made sense for him.

He has more money than he can spend. The Heat give him a chance for an easy ring at the end of his career. He doesn’t have to work as hard to get open. In Miami, he’s not riding the bench to make room for Avery Bradley. Plus, some folks claim the weather in South Beach is superior to Eastern Massachusetts.

But booing Damon never made sense to me. Ditto for Papelbon. They gave Boston championships. They were clutch. They wanted the ball in the big games. And the Sox passed on their future services when free agency beckoned. Just like the Pats with Vinatieri.

Youk had no choice in his departure from Boston. He was dealt for a bag of baseballs last summer. When he came back to haunt the Red Sox with the White Sox, fans didn’t seem to mind. It seemed like a vote for Youk was a vote against Bobby Valentine and the bumbling Sox leadership in 2012.

“I think that was a whole other situation,’’ said Youkilis. “Every time I got a hit against the Red Sox last summer, I think Sox fans were pretty happy. It just shows Johnny’s experience was different. My experience was different.’’

It will be different when he returns with the Yankees July 19.

“I’ll get booed, no doubt,’’ said Youk, who had an RBI single in the fifth Friday night. “Fans are fans.’’

Fortunately (or unfortunately), it’s hard to tell when it comes to Youk. The sound of 30,000 people saying “Yoooooouk’’ is virtually indistinguishable from the sound of 30,000 fans booing.

“A lot of Red Sox fans come up to me and they are very thankful and wish I was on the Red Sox,’’ said Youk. “It just depends.

“When I played in Boston, there’s probably a few Boston fans that didn’t like me, and so be it. You can’t win over everybody in the room. I’ve learned that as I got older.

“For me, I just had to move on. There’s 29 other teams out there and you’ve got to put yourself in the best-case scenario and move on. Right now, I’m trying to win another World Series and I thought this was the best team possible.’’